1. Field of the Invention
The present invention relates to noncontact electric power feeding apparatus and method for feeding an electric power by using a resonance such as a magnetic field resonance or an electric field resonance, noncontact electric power receiving apparatus and method for receiving the electric power by using the resonance such as the magnetic field resonance or the electric field resonance, and a noncontact electric power feeding system for feeding the electric power by using the resonance such as the magnetic field resonance or the electric field resonance.
2. Description of the Related Art
An electromagnetic induction system and a magnetic field resonance system are each known as a technique for enabling an electric energy to be transmitted in a noncontact style. Also, the electromagnetic induction system and the magnetic field resonance system are different in various respects from each other. In recent years, the energy transmission using the magnetic field resonance system attracts attention.
FIG. 8 is a conceptual diagram, partly in circuit, showing a basic configuration of a noncontact electric power feeding system using the magnetic field resonance system. The noncontact electric power feeding system using magnetic field resonance system is composed of an electric power feeding side (electric power feeding apparatus) 100, and an electric power receiving side (electric power receiving apparatus) 200.
The electric power feeding side 100 includes an A.C. power source 101 and a resonance element 102. The A.C. power source 101 generates an A.C. electric power (A.C. current) having the same self-resonance frequency as that of the resonance element 102 and supplies the A.C. electric power thus generated to the resonance element 102.
The electric power receiving side 200 is composed of a resonance element 201 and a load circuit 202. The resonance element 101 of the electric power feeding side 100 and the resonance element 201 of the electric power receiving side 200 are identical in self-resonance frequency to each other, and are coupled to each other through magnetic field coupling.
Therefore, the A.C. electric power generated by the A.C. power source 102 of the electric power feeding side 100 is supplied to the resonance element 102, thereby generating the magnetic field in the resonance element 102. Also, the magnetic field coupling is caused between the resonance element 102 of the electric power feeding side 100, and the resonance element 201 of the electric power receiving side 200 to induce the A.C. electric power in the resonance element 201 of the electric power receiving side 200. The A.C. electric power thus induced is supplied to the load circuit 202.
However, in the case of the noncontact electric power feeding system using the magnetic field resonance system shown in FIG. 8, in the electric power feeding side 100, reflection of the electric power is caused between the A.C. power source 101 and the resonance element 102. Likewise, in the electric power receiving side 200, the reflection of the electric power is caused between the resonance element 201 and the load circuit 202. For this reason, it may be impossible to efficiently carry out the power transmission.
In addition, in the noncontact electric power feeding system using the magnetic field resonance system, normally, an unmodulated sine wave having a central frequency fo is used as the A.C. power. Since this unmodulated sine wave is unmodulated one, an occupied frequency bandwidth is narrow (ideally 0 (zero) Hz).
Therefore, a frequency band necessary for the resonance coil through which the unmodulated sine wave is transmitted has to be as narrow as about several hertz. However, for the purpose of increasing a transmission efficiency, it is required for a resonance circuit that a loss is low (“a Q value” is large). Here, it is noted that “the Q value” represents the sharpness of the peak of the resonance in the resonance circuit, and thus when the peak of the resonance becomes sharp, it is possible to increase the transmission efficiency of the A.C. electric power.
In a word, in order to obtain the high transmission efficiency in the noncontact electric power transmission using the magnetic field resonance system, it is preferable to increase the Q value as much as possible in both the resonance element 102 of the electric power feeding side 100, and the resonance element 201 of the electric power receiving side 200.
As shown in FIG. 8, however, when the resonance element 102 is directly connected to the A.C. power source 101 on the electric power feeding side 100, the Q value of the resonance element 102 is reduced due to the influence of circuit impedance. Likewise, when the resonance element 201 is directly connected to the A.C. load circuit 202 on the electric power receiving side 200 as well, the Q value of the resonance element 201 is reduced due to the influence of circuit impedance.
Then, for the purpose of preventing both the reflection of the electric power, and the reduction of the Q value, there is adopted a configuration such that excitation elements are used in both the electric power feeding side 100 and the electric power receiving side 200, respectively.
FIG. 9 is a block diagram showing an example of a configuration of a noncontact electric power feeding system, using a magnetic field resonance system, which is configured in order to prevent both the reflection of the electric power, and the reduction of the Q value by providing excitation elements in both the electric power feeding side 100 and the electric power receiving side 200, respectively.
As shown in FIG. 9, the electric power feeding side 100 has a configuration such that an excitation element 103 is provided between the A.C. power source 101 and the resonance element 102. The electric power receiving side 200 has a configuration such that an excitation element 203 and a rectifying circuit 204 are provided between the resonance element 201 and the load circuit 202.
Here, the electric power feeding side 100, for example, is realized in the form of a charging apparatus or the like. Also, the electric power receiving side 200, for example, is realized in the form of a mobile electronic apparatus such as a mobile-phone unit.
Also, the inside of the electric power feeding side 100 is configured in such a way that the excitation element 103 is connected to the A.C. power source 101, and the excitation element 103 and the resonance element 102 are strongly coupled to each other through the electromagnetic induction. Likewise, the inside of the electric power receiving apparatus 200 is configured in such a way that the resonance element 201 and the excitation element 203 are strongly coupled to each other through the electromagnetic induction, the excitation element 203 is connected to the rectifying circuit 204, and the rectifying circuit 204 and the load circuit 202 are connected to each other.
Also, similarly to the case of the noncontact electric power transmission system shown in FIG. 8 when the resonance element 102 of the electric power feeding side 100, and the resonance element 201 of the electric power receiving side 200 agree in self-resonance frequency to each other, the resonance element 102 of the electric power feeding side 100, and the resonance element 201 of the electric power receiving side 200 show a magnetic field resonance relationship. As a result, a coupling amount becomes maximum, and a loss becomes minimum.
That is to say, in the noncontact electric power feeding system shown in FIG. 9, firstly, in the electric power feeding side 100, an A.C. electric power (A.C. current) having a predetermined frequency is supplied from the A.C. power source 101 to the excitation element 103, which results in that an A.C. electric power is induced in the resonance element 102 through the electromagnetic induction. Here, a frequency of the A.C. electric power generated in the A.C. power source 101 is set as being identical to each of a self-resonance frequency of the resonance element 102 of the electric power supply source, and a self-resonance frequency of the resonance element 201 of the electric power supply destination.
Also, as described above, the resonance element 102 of the electric power feeding side 100, and the resonance element 201 of the electric power receiving side 200 are disposed so as to show the magnetic field resonance relationship. Thus, the A.C. electric power is supplied from the resonance element 102 to the resonance element 201 at a resonance frequency in a noncontact style.
In the electric power receiving side 200, the A.C. electric power supplied from the resonance element 102 of the electric power feeding side 100 is received by the resonance element 201. The A.C. electric power from the resonance element 201 is supplied to the rectifying circuit 204 via the excitation element 203 through the electromagnetic induction, and is then converted into a D.C. electric power (D.C. current) in the rectifying circuit 204 to be supplied to each of the various kinds of load circuits 202.
In the manner described above, the D.C. electric power is supplied from the electric power feeding side 100 to the electric power receiving side 200 in the noncontact style. It is noted that the D.C. electric power outputted from the rectifying circuit 204, for example, is supplied to a charging circuit as the load circuit 202 to which a battery is connected, thereby being used to charge the battery with the electricity.
Also, the following features are obtained in the noncontact electric power feeding system in which the electric power feeding side and the electric power receiving side which are configured in the manner as shown in FIG. 9 show one-to-one correspondence.
The noncontact electric power feeding system concerned has a relationship, as shown in FIG. 10, between the frequency of the A.C. power source and the coupling amount. As can be seen from FIG. 10, even when the frequency of the A.C. power source is low, or conversely the frequency of the A.C. power source is high, the coupling amount does not become large. Thus, the coupling amount becomes maximum only at a specific frequency at which a magnetic field resonance phenomenon is caused. That is to say, the magnetic field resonance allows the frequency property of the coupling amount to show a frequency selectivity property.
In addition, the noncontact electric power feeding system concerned has a relationship, as shown in FIG. 11, between a distance between the resonance elements 102 and 201, and the coupling amount. As can be seen from FIG. 12, the coupling amount is reduced as the distance between the resonance elements 102 and 201 becomes longer.
However, the coupling amount does not become large just because the distance between the resonance elements 102 and 201 is short. Thus, the distance at which the coupling amount becomes maximum exists at a certain resonance frequency. In addition, as apparent from FIG. 11, it is also possible to ensure a certain or more coupling amount as long as the distance between the resonance elements 102 and 201 falls within a certain range.
In addition, the noncontact electric power feeding system has a relationship, as shown in FIG. 12, between the resonance frequency and the inter-resonance element distance at which the maximum coupling amount is obtained. That is to say, it is understood from FIG. 12 that when the resonance frequency is low, the resonance element interval is wide. In addition, it is also understood from FIG. 12 that when the resonance frequency is high, the maximum coupling amount can be obtained by narrowing the resonance element interval.
In the noncontact electric power feeding system using the electromagnetic induction system which has been currently widely used, the electric power feeding side and the electric power receiving side need to have a magnetic flux in common. For the purpose of efficiently feeding the electric power, the electric power feeding source and the electric power feeding destination need to be disposed close proximity to each other, and thus the axis alignment for the coupling between the electric power feeding source and the electric power feeding destination becomes also important.
On the other hand, the noncontact electric power feeding system using the magnetic field resonance phenomenon, as described above, has an advantage that from the principles called the magnetic field resonance phenomenon, the electric power can be transmitted at a longer distance than that in the case of the noncontact electric power feeding system using the electromagnetic induction system, and even when the axis alignment is slightly poor, the electric power transmission efficiency is not reduced so much.
Note that, US Patent Application Publication No. 2007/0222542 discloses a technique about an electric power transmission system using the magnetic field resonance system as described above.